Insect Repellent

Jai Ganesh · Yesterday 23:21:25

Insect Repellent

Gist

What is an insect repellent?

Not only are they irritating, but many insects are also carriers of dangerous diseases such as malaria, dengue, Zika virus, and Lyme disease. This is where insect repellents come into play. Insect repellents are substances designed to keep insects away from humans, reducing the chance of bites and disease transmission.

For more than 60 years, DEET has reigned as the undisputed champion of insect repellents. No longer. There's now a potentially better alternative on the market: picaridin. Both DEET and picaridin are proven to be effective at fending off ticks—and are superior to other repellents when it comes to protection time.

(N,N-Diethyl-meta-toluamide, also called diethyltoluamide or DEET).

Summary

The 3 major reasons to use insect repellents are: 1) new threats to human health posed by emerging and imported arthropod-borne infectious diseases; 2) the dominance of new, competent insect vectors of infectious diseases; and 3) the inability to primarily prevent the transmission of most arthropod-borne infection diseases by vaccinations with the exceptions of yellow fever vaccine in South America and Africa, Japanese encephalitis vaccine in Southeast Asia, and several regional tick-borne virus vaccines in Eastern Europe.

For many people, applying insect repellents may be the most effective and easiest way to protect against arthropod bites. The search for the ‘perfect’ insect repellent has been ongoing for decades, and has yet to be achieved. The ideal agent would: repel multiple species of biting arthropods; remain effective for at least 8 h; cause no irritation to skin or mucous membranes; possess no systemic toxicity; be resistant to abrasion and washoff; and be greaseless and odorless. No presently-available insect repellent meets all of these criteria. Efforts to find such a compound have been hampered by the multiplicity of variables that affect the inherent repellency of any chemical. Repellents do not all share a single mode of action, and different species of insects may react differently to the same repellent.

To be effective as an insect repellent, a chemical must be volatile enough to maintain an effective repellent vapor concentration at the skin surface, but not evaporate so rapidly that it quickly loses its effectiveness. Multiple factors play a role in effectiveness, including concentration, frequency and uniformity of application, the user's activity level and inherent attractiveness to blood-sucking arthropods, and the number and species of the organisms trying to bite. Gender may also play a role in how well a repellent works – one study has shown that DEET-based repellents worked less well in women than in men. The effectiveness of any repellent is reduced by abrasion from clothing; evaporation and absorption from the skin surface; washoff from sweat, rain, or water; and a windy environment. Each 10°C increase in ambient temperature can lead to as much as 50% reduction in protection time, due to greater evaporative loss of the repellent from the skin surface. One of the greatest limitations of insect repellents is that they do not ‘cloak’ the user in a chemical veil of protection; any untreated exposed skin will be readily bitten by hungry arthropods.

Details

An insect repellent (also commonly called "bug spray" or "bug deterrent") is a substance applied to the skin, clothing, or other surfaces to discourage insects (and arthropods in general) from landing or climbing on that surface. Insect repellents help prevent and control the outbreak of insect-borne (and other arthropod-bourne) diseases such as malaria, Lyme disease, dengue fever, bubonic plague, river blindness, and West Nile fever. Pest animals commonly serving as vectors for disease include insects such as flea, fly, and mosquito; and ticks (arachnids).

Some insect repellents are insecticides (bug killers), but most simply discourage insects and send them flying or crawling away.

Effectiveness

Synthetic repellents tend to be more effective and/or longer lasting than "natural" repellents.

For protection against ticks and mosquito bites, the U.S. Centers for Disease Control (CDC) recommends DEET, icaridin (picaridin, KBR 3023), oil of lemon eucalyptus (OLE), para-menthane-diol (PMD), IR3535 and 2-undecanone with the caveat that higher percentages of the active ingredient provide longer protection.

In 2015, researchers at New Mexico State University tested 10 commercially available products for their effectiveness at repelling mosquitoes. The known active ingredients tested included DEET (at various concentrations), geraniol, p-menthane-3-8-diol (found in lemon eucalyptus oil), thiamine, and several oils (soybean, rosemary, cinnamon, lemongrass, citronella, and lemon eucalyptus). Two of the products tested were fragrances where the active ingredients were unknown. On the mosquito Aedes aegypti, only one repellent that did not contain DEET had a strong effect for the duration of the 240 minutes test: a lemon eucalyptus oil repellent. However, Victoria's Secret Bombshell, a perfume not advertised as an insect repellent, performed effectively during the first 120 minutes after application.

In one comparative study from 2004, IR3535 was as effective or better than DEET in protection against Aedes aegypti and Culex quinquefasciatus mosquitoes. Other sources (official publications of the associations of German physicians as well as of German druggists) suggest the contrary and state DEET is still the most efficient substance available and the substance of choice for stays in malaria regions, while IR3535 has little effect. However, some plant-based repellents may provide effective relief as well. Essential oil repellents can be short-lived in their effectiveness.

A test of various insect repellents by an independent consumer organization found that repellents containing DEET or icaridin are more effective than repellents with "natural" active ingredients. All the synthetics gave almost 100% repellency for the first 2 hours, where the natural repellent products were most effective for the first 30 to 60 minutes, and required reapplication to be effective over several hours.

Although highly toxic to cats, permethrin is recommended as protection against mosquitoes for clothing, gear, or bed nets. In an earlier report, the CDC found oil of lemon eucalyptus to be more effective than other plant-based treatments, with a similar effectiveness to low concentrations of DEET. However, a 2006 published study found in both cage and field studies that a product containing 40% oil of lemon eucalyptus was just as effective as products containing high concentrations of DEET. Research has also found that neem oil is mosquito repellent for up to 12 hours. Citronella oil's mosquito repellency has also been verified by research, including effectiveness in repelling Aedes aegypti, but requires reapplication after 30 to 60 minutes.

There are also products available based on sound production, particularly ultrasound (inaudibly high-frequency sounds) which purport to be insect repellents. However, these electronic devices have been shown to be ineffective based on studies done by the United States Environmental Protection Agency and many universities.

Safety issues:

For humans

Children may be at greater risk for adverse reactions to repellents, in part, because their exposure may be greater. Children can be at greater risk of accidental eye contact or ingestion. As with chemical exposures in general, pregnant women should take care to avoid exposures to repellents when practical, as the fetus may be vulnerable.

Some experts also recommend against applying chemicals such as DEET and sunscreen simultaneously since that would increase DEET penetration. Canadian researcher, Xiaochen Gu, a professor at the University of Manitoba's faculty of Pharmacy who led a study about mosquitos, advises that DEET should be applied 30 or more minutes later. Gu also recommends insect repellent sprays instead of lotions which are rubbed into the skin "forcing molecules into the skin".

Regardless of which repellent product used, it is recommended to read the label before use and carefully follow directions. Usage instructions for repellents vary from country to country. Some insect repellents are not recommended for use on younger children.

In the DEET Reregistration Eligibility Decision (RED) the United States Environmental Protection Agency (EPA) reported 14 to 46 cases of potential DEET associated seizures, including 4 deaths. The EPA states: "... it does appear that some cases are likely related to DEET toxicity", but observed that with 30% of the US population using DEET, the likely seizure rate is only about one per 100 million users.

The Pesticide Information Project of Cooperative Extension Offices of Cornell University states that, "Everglades National Park employees having extensive DEET exposure were more likely to have insomnia, mood disturbances and impaired cognitive function than were lesser exposed co-workers".

The EPA states that citronella oil shows little or no toxicity and has been used as a topical insect repellent for 60 years. However, the EPA also states that citronella may irritate skin and cause dermatitis in certain individuals. Canadian regulatory authorities concern with citronella based repellents is primarily based on data-gaps in toxicology, not on incidents.

Within countries of the European Union, implementation of Regulation 98/8/EC, commonly referred to as the Biocidal Products Directive, has severely limited the number and type of insect repellents available to European consumers. Only a small number of active ingredients have been supported by manufacturers in submitting dossiers to the EU Authorities.

In general, only formulations containing DEET, icaridin (sold under the trade name Saltidin and formerly known as Bayrepel or KBR3023), IR3535 and citriodiol (p-menthane-3,8-diol) are available. Most "natural" insect repellents such as citronella, neem oil, and herbal extracts are no longer permitted for sale as insect repellents in the EU due to their lack of effectiveness; this does not preclude them from being sold for other purposes, as long as the label does not indicate they are a biocide (insect repellent).

Toxicity for other animals

A 2018 study found that icaridin is highly toxic to salamander larvae, in what the authors described as conservative exposure doses. The LC50 standard was additionally found to be completely inadequate in the context of finding this result.

Permethrin is highly toxic to cats but not to dogs or humans.

Additional Information

Warmer weather means more chances for kids to go outside to play, hike and enjoy the fresh air with family and friends. Warmer weather also means preventing insect bites.

Biting insects such as mosquitoes and biting flies can make children miserable. More worrisome is that bites from some insects can cause serious illnesses.

Preventing insect bites

Depending on where you live, you may already be familiar with illnesses that spread from insects to people. For example, Lyme disease, West Nile disease and Zika spread through the bite of a mosquito or tick. Recently, these insect-borne illnesses have been on the rise due, in part, to the effects of climate change.

One way to protect your child from biting insects is to use insect repellents. Choose an insect repellent that is effective at preventing bites from insects commonly found where you live. Follow the instructions on the label for proper use.

Keep in mind that most insect repellents don't kill insects. Insects that bite—not insects that sting—are kept away by repellents. Biting insects include mosquitoes, ticks, fleas, chiggers and biting flies. Stinging insects include bees, hornets and wasps.

Insect repellents approved as safe and effective

The American Academy of Pediatrics and Centers for Disease Control and Prevention recommend using an insect repellent product that has been registered by the Environmental Protection Agency (EPA). These products contain ingredients such as DEET, picaridin, oil of lemon eucalyptus or another EPA-registered active ingredient. Use this tool to search for EPA-registered insect repellents.

DEET

Several insect repellents with DEET are approved as safe and effective. The concentration of DEET in a product affects how long the product will be effective. You can choose the lowest concentration to provide protection for the among of time spent outside.

For example, 10% DEET provides protection for about 2 hours, and 30% DEET protects for about 5 hours. A higher concentration works for a longer time, but anything over 50% DEET does not provide longer protection.

DEET products can cause skin rashes especially when high concentrations are used, but these reactions are rare.

Until infants and children are at least 2 years old, their skin may be different than the skin of an older child or adult. Apply DEET sparingly when needed. Weigh the risks of exposure to potentially serious illness spread by insects and the possible risk of absorbing chemicals into the body.

Parents of newborns and premature infants should be especially cautious when deciding whether to apply DEET or other chemicals on their child's skin.

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Insect Repellent

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